1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a method and apparatus for transmitting and receiving a status report of Automatic Repeat reQuest (ARQ) in an ARQ layer.
2. Description of the Related Art
The Universal Mobile Telecommunication Service (UMTS) system, which is a 3rd Generation (3G) asynchronous mobile communication system, uses Wideband Code Division Multiple Access (WCDMA). UMTS is based on Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS), both of which are European mobile communication systems.
Within the 3rd Generation Partnership Project (3GPP) in charge of UMTS standardization, Long Term Evolution (LTE) is being discussed as the next generation mobile communication system of the UMTS system. LTE, aimed for deployment in around 2010, is a technology for implementing high-speed packet based communication at about 100 Mbps. To this end, several schemes are under discussion, including one scheme for reducing the number of nodes located in a communication path by simplifying the network configuration, and another scheme for maximally implementing wireless protocols to wireless channels.
FIG. 1 is an overview of a configuration of an Evolved UMTS (E-UMTS) mobile communication system.
Referring to FIG. 1, a configuration of Evolved UMTS Radio Access Networks (E-UTRANs or E-RAN) 135 and 140 is simplified to a 2-node configuration of Evolved Node Bs (ENBs or Node Bs) 110 to 130, and anchor nodes 145 and 150. A User Equipment (UE) 105 accesses an Internet Protocol (IP) network by E-RAN 135 and 140.
ENBs 110 to 130, nodes corresponding to the existing Node Bs, are connected to UE 105 over a wireless channel. Compared with the existing Node Bs, ENBs 110 to 130 perform more complex functions.
In LTE, all user traffics, including real-time services such as Voice over IP (VoIP) service, are serviced over a shared channel. This means that there is a need for an apparatus for collecting status information of UEs and performing scheduling depending thereon, and the scheduling is managed by ENBs 110 to 130. The terms ‘ENB’ and ‘Node B’ are herein used interchangeably.
In LTE, like in High Speed Downlink Packet Access (HSDPA) or Enhanced Uplink Dedicated Channel (EDCH), Hybrid Automatic Repeat reQuest (HARQ) is performed between ENBs 110 to 130 and UE 105. However, with use of only the HARQ, LTE cannot satisfy the various Quality of Service (QoS) requirements. Therefore, a separate ARQ (or outer-ARQ) can be performed in an upper layer, and outer-ARQ is also performed between ENBs 110 to 130 and UE 105.
It is expected that LTE will use Orthogonal Frequency Division Multiplexing (OFDM) as wireless access technology in a 20-MHz bandwidth in order to realize a data rate of a maximum of 100 Mbps. In addition, LTE will employ Adaptive Modulation & Coding (AMC) that determines a modulation scheme and a channel coding rate according to channel status of UEs. Many mobile communication systems now under discussion, including LTE, use both HARQ and ARQ as an error correction technique.
HARQ is a technique for soft-combining previously received data with retransmitted data without discarding the previously received data, thereby increasing the reception success rate. More specifically, an HARQ receiving (Rx) entity determines presence/absence of error in a received packet, and sends an Acknowledged (ACK) signal or a Non-Acknowledged (NACK) signal to an HARQ transmitting (Tx) entity according to the presence/absence of error. The HARQ Tx entity performs retransmission of the HARQ packet or transmission of a new HARQ packet according to the HARQ ACK/NACK signal. HARQ is characterized in that it soft-combines a retransmitted packet with a previously received packet, thereby reducing the error rate.
However, ARQ, a technique for checking the sequence number of a received packet and sending the retransmission request for a missing packet using a status report, does not soft-combine a previously received packet with a retransmitted packet.
Because both ARQ and HARQ have a function of recovering erroneous packets, it is considered that there is no need to perform ARQ and HARQ together. However, because a sufficiently low packet error ratio cannot be obtained with only using HARQ, ARQ and HARQ should be performed together in most packet services.
In HARQ, because an HARQ ACK/NACK signal is a 1-bit response signal, it is difficult to reduce the error rate through channel coding. Therefore, it is hard to achieve a low packet error rate with use of only HARQ. That is, if an HARQ NACK signal is misrecognized as an HARQ ACK signal, the corresponding packet is completely lost at the HARQ layer. Therefore, reliability of the HARQ ACK/NACK signal acts as an important factor in determining a packet error ratio in the HARQ layer.
The system, in which ARQ and HARQ operate together, can increase efficiency of an ARQ operation using information from the HARQ layer. For example, an HARQ Tx entity sends transmission complete time information for an ARQ packet to an ARQ transmitting (Tx) entity, and the ARQ Tx entity compares the time the status report has occurred, with the time the ARQ packet transmission is completed, thereby preventing unnecessary retransmission.
If occurrence and transmission of the status report are achieved during the same time, the time the HARQ packet containing the status report was initially received is substantially equal to the time the status report has occurred. However, if the occurrence time of the status report is different from the transmission time of the status report, the ARQ Tx entity cannot estimate the occurrence time of the status report, and merely recognizes, as the occurrence time of the status report, the time the HARQ packet containing the status report was initially received.
For example, reception of success/failure information for specific ARQ packet(s), received for a delayed time from the occurrence time to the transmission time of the status report at the ARQ receiving (Rx) entity, cannot be included in the previously generated status report. Because the status report has no reception of success/failure information for the specific ARQ packet, the ARQ Tx entity retransmits the specific ARQ packet to the ARQ Rx entity, considering that it has failed to transmit the specific ARQ packet. Therefore, the conventional mobile communication system may experience unnecessary retransmission.